A refrigeration and air-conditioning apparatus has been known which detects leakage of a refrigerant from a refrigerant circuit of the refrigeration and air-conditioning apparatus by calculating the refrigerant density of individual elements (driving devices (actuators) such as a compressor and an expansion valve) forming a refrigeration cycle on the basis of detection results of a pressure sensor and a temperature sensor used for controlling the elements and calculating the amount of refrigerant within the refrigerant circuit by adding up the internal volumes of the elements (see, for example, Patent Literature 1).
The amount of refrigerant necessary for operation differs according to the operation conditions of the refrigeration and air-conditioning apparatus. Therefore, a liquid reserve container for reserving excess refrigerant may be installed. Such a liquid reserve container is installed on a high-pressure side or low-pressure side of the refrigerant circuit. In order to detect refrigerant leakage from the refrigerant circuit, it is necessary to calculate the amount of refrigerant in the individual elements forming the refrigeration and air-conditioning apparatus.
The state of a refrigerant in the element devices other than the liquid reserve container can be estimated from existing sensor measurement values, such as pressure and temperature, used for an operation of the refrigeration and air-conditioning apparatus. Thus, the amount of refrigerant in such element devices can be calculated. In contrast, the state of a refrigerant in the liquid reserve container does not change irrespective of the amount of refrigerant, and therefore the amount of refrigerant in the liquid reserve container cannot be calculated from existing sensor measurement values. Accordingly, for the liquid reserve container, after a change occurs in the internal state of the liquid reserve container, for example, after a liquid refrigerant in the liquid reserve container has become empty, abnormality, that is, a shortage of refrigerant and refrigerant leakage, are detected.
However, in the case where a state in which the amount of liquid refrigerant existing inside the liquid reserve container is more than half the total filled amount often occurs and the method described in Patent Literature 1 for detecting refrigerant leakage after excess liquid refrigerant has become empty is used, a large amount of refrigerant leaks into the air.
Under such circumstances, as measures to identify the excess liquid amount so that refrigerant leakage can be detected as early as possible, the liquid reserve container is provided with a window or a float-type sensor for measuring the liquid level is installed inside the liquid reserve container.
However, in order to identify the excess liquid amount in an existing apparatus by using the above measures, such as providing the liquid reserve container with a window or installing a sensor in the liquid reserve container, processing for installing the window or the sensor at the existing apparatus is required. In actuality, it is very difficult to perform such processing. Even if such processing is possible, modifying the liquid reserve container, in which the pressure inside the device is greatly variable, reduces the withstand pressure and thus greatly affects the reliability. Furthermore, an operation for making a hole or a window is complicated and takes time and effort, and a problem such as increasing the cost occurs.
A technology for detecting refrigerant leakage is suggested in which a liquid level detection sensor using ultrasonic waves is disposed outside the liquid reserve container so that the liquid level height inside the liquid reserve container can be detected by the liquid level detection sensor, while the refrigerant density is obtained on the basis of the temperature of the refrigerant to convert the liquid level height into the amount of excess liquid refrigerant using the liquid density or the like (see, for example, Patent Literature 2). With this technology, even if excess liquid refrigerant is reserved inside the liquid reserve container, the amount of the excess liquid amount can be detected. Therefore, the total amount of refrigerant inside the refrigeration and air-conditioning apparatus can be calculated. Thus, it is possible to detect refrigerant leakage early.
In addition, a method for identifying the amount of excess liquid refrigerant inside the liquid reserve container by identifying the liquid level position of the amount of excess liquid refrigerant has been known. A method for identifying the liquid level inside the liquid reserve container has been known in which a plurality of sensors each including a heater, a temperature sensor, and a protection layer are used and the heaters are heated up so that the liquid level inside the liquid reserve container can be identified on the basis of a difference in the temperature between a liquid refrigerant and a gas refrigerant existing inside the liquid reservoir (see, for example, Patent Literature 3).
Furthermore, a technology has been known in which a temperature sensor is installed outside the liquid reserve container so that the liquid level inside the liquid reserve container can be identified in the case where there is a difference in the temperature between a concentrated solution and a vapor inside the liquid reserve container (see, for example, Patent Literature 4).